In recent years, advances in technology, as well as ever evolving tastes in style, have led to substantial changes in the design of automobiles. One of the changes involves the power usage and complexity of the various electrical systems within automobiles, particularly alternative fuel vehicles, such as hybrid, electric, and fuel cell vehicles.
Many electric-powered vehicles require a high primary operating voltage, e.g., 400 volts DC. Typical fuel cells provide less than one volt DC under load. Therefore, a large number of individual fuel cells are often configured or “stacked” in series to provide a fuel cell stack capable of providing the high primary operating voltage required by the vehicle. Additionally, most fuel cell vehicles and/or systems are designed to provide all of the traction power for vehicle operation from the fuel cell stack. This results in overdesign of the fuel cell stack because it must provide the peak power needed for the vehicle. Often, sufficient stacking of fuel cells is not practical in many high-voltage applications due to cost and packaging constraints.
Power converters, such as direct current-to-direct current (DC/DC) boost converters, are typically used to raise the voltage level of a fuel cell stack and reduce the number of individual fuel cells needed in the vehicle. Often, a high-voltage battery is utilized to provide the peak power to the vehicle during periods of operation requiring traction power in excess of what the fuel cell stack can provide. The high-voltage battery may be recharged by the fuel cell stack when the vehicle traction drive unit does not require peak power. However, the high-voltage battery limits the voltage range at the converter output, and therefore these designs are inefficient during light loading conditions where vehicle does not require such high voltage.